rust: samples: add missing newlines in rust_print_main

Calls to `pr_info!` in `arc_print` are missing trailing newlines, which
are expected as the `pr_*!` documentation shows.

Add the missing `\n` to all four formatting strings.

Fixes: f431c5c581 ("samples: rust: print: Add sample code for Arc printing")
Fixes: 47cb6bf786 ("rust: use derive(CoercePointee) on rustc >= 1.84.0")
Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1139
Signed-off-by: Mehmet Koseoglu <mehmet.mkoseoglu@gmail.com>
Link: https://patch.msgid.link/20260828015148.221737-2-mehmet.mkoseoglu@gmail.com
[ Reworded to fix the description of the missing-newline behavior. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

samples/rust/rust_print_main.rs

@@ -23,10 +23,10 @@ fn arc_print() -> Result {
     let b = UniqueArc::new("hello, world", GFP_KERNEL)?;
 
     // Prints the value of data in `a`.
-    pr_info!("{}", a);
+    pr_info!("{}\n", a);
 
     // Uses ":?" to print debug fmt of `b`.
-    pr_info!("{:?}", b);
+    pr_info!("{:?}\n", b);
 
     let a: Arc<&str> = b.into();
     let c = a.clone();
@@ -42,7 +42,7 @@ fn arc_print() -> Result {
 
         use kernel::fmt::Display;
         fn arc_dyn_print(arc: &Arc<dyn Display>) {
-            pr_info!("Arc<dyn Display> says {arc}");
+            pr_info!("Arc<dyn Display> says {arc}\n");
         }
 
         let a_i32_display: Arc<dyn Display> = Arc::new(42i32, GFP_KERNEL)?;
@@ -53,7 +53,7 @@ fn arc_print() -> Result {
     }
 
     // Pretty-prints the debug formatting with lower-case hexadecimal integers.
-    pr_info!("{:#x?}", a);
+    pr_info!("{:#x?}\n", a);
 
     Ok(())
 }